Tom's Blog

Friday, September 26, 2008

Milkweed bugs

This year seems to be a banner year for milkweed bugs. They are all over the milkweed pods, piercing a pod wall and sucking the juices out of the milkweed seeds. We have had these in small numbers before, but never in the numbers we are seeing this year. I assume that the very wet weather we had earlier this summer is responsible. (It's tempting to blame that awful weather for almost everything!)

Milkweed bugs are easy to raise and because of this are used in quite a few undergraduate biology courses. That's fine, but I'm not happy about them decimating our milkweed seed pods. We get few enough pods as it is, and I hate to lose good seeds to this specialized grazer.

Milkweed bugs are themselves relatively resistant to attack by birds or other predators. The reason is that milkweed bugs are full of the toxic alkaloids that milkweed plants produce. If a bird takes a taste of a milkweed bug, it is immediately repelled by the awful taste. After a while the bird learns to recognize these bugs and doesn't even try to eat them.

I am most concerned about the effect milkweed bugs might have on purple milkweed (Asclepias purpurascens), our endangered species. We have had a substantial infestation in our forbs garden, but so far the plants in the field have not been affected. However, I have seen them in the field on poke milkweeds, a species that has a similar habitat to purple milkweed.

It's not surprising to see these large infestations, as the female can lay as many as 30 eggs a day and up to 9000 eggs during her lifetime.

I was amused to note that in the biology classes they don't even need milkweeds, as they can raise milkweed bugs on cracked seeds of sunflower, watermelon, squash, etc.


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